Projection lens unit

ABSTRACT

A projection lens unit, which is small, compatible and highly capable of compensating for the changes in temperature, is provided. The unit comprises a coupler  5  provided at the front surface of a CRT  1 , a lens unit body  6  for projecting an image onto a screen by controlling and magnifying the light from the CRT  1 , a plurality of leg portions  7  secured to the coupler  5  for supporting the lens unit body  6  at more than three points, a slide mechanism (latches  58  and latch engaging slots  42 ) provided between the leg portions  7  and the lens unit body  6  for slidably supporting the leg portions  7  in the direction of optical axis in relation to the lens unit body  6 , and an expansion/contraction bars  8  provided between the leg portions  7  and the lens unit body  6  for compensating for the effect of heat with one end engaged with the tip end side of the leg portions  7  and the other end with the base end side of the lens unit body  6.

TECHINICAL BACKGROUD

[0001] The present invention generally relates to a projection lens unit which is used in a projector and the like for projecting an image at the light source side and the like onto a screen and the like, and, more specifically to a projection lens unit provided with a function of automatically compensating for an effect of heat.

[0002] Recent years, as images are becoming increasingly highly defined on a projector and the like as can be seen in a high-vision image, consistent quality of the projected images (image quality) is required. Accordingly, a high performance is required of projection lens units also. However, in maintaining the high quality of the projection lens unit, the effect of heat becomes a problem.

[0003] When the projection lens unit is provided to the place close to the light source, heat of the light source becomes an issue. The ambient temperature also has an effect on the quality. Specifically, the effect of thermal expansion and thermal contraction induced by heat of the light source and the ambient temperature changes the spacing or refractive index of each lens and the cylindrical body which supports the lenses. When these are changed in a projector and the like, the image on the screen becomes blurred and deteriorated.

[0004] In order to solve such problems, U.S. Pat. Nos. 4,525,745 and 5,731,917 have been disclosed.

[0005] In U.S. Pat. No. 4,525,745, a piece of power lens is supported by a bimetal ring and compensation for the thermally induced changes is achieved by causing the power lens to shift using its characteristics to change with temperature.

[0006] U.S. Pat. No. 5,731,917 comprises mainly a cathode ray tube 100 and a projection lens unit 101. The projection lens unit 101 is provided with an inner tube 102, an outer tube 103 and a bimetal 104.

[0007] The inner tube 102 supports a plurality of lenses 105 therein. On the periphery of the inner tube 102, frictional contact chips 106 are provided, which are slidably contacted with the inner periphery of the outer tube 103. The inner tube 102 is slidably supported on the outer tube 103 by the frictional contact chips 106. Further, on the periphery of the inner tube 102, a guide member 107 is provided at one end of the bimetal 104, extending outwardly from the outer tube 103.

[0008] The outer tube 103 is secured to the cathode ray tube 100 side. Inside the outer tube 103, the inner tube 102 is slidably supported. The inside diameter of the outer tube 103 is designed to be larger than the outside diameter of the inner tube 102, thereby defining a space between the outer tube 103 and the inner tube 102 to which the bimetal 104 is inserted.

[0009] The bimetal 104 is mounted to the guide member 107 of the inner tube 102 at one end, and to the outer tube 103 side at the other end.

[0010] In this construction, as the bimetal 104 is distorted by the temperature changes, the inner tube 102 slides with being supported on the outer tube 103, thereby enabling an adjustment of the positions of the lenses 105.

[0011] Meantime, in U.S. Pat. No. 4,525,745, an adjustment is done on just one piece of power lens by the bimetal ring. However, in many cases, it is not possible to obtain a clear image just by adjusting only one piece of power lens because the effect of heat extends to various parts.

[0012] Further, U.S. Pat. No. 5,731,917 has the following drawbacks.

[0013] (1) Where the inner tube 102 is shifted through the power of the bimetal 104 generated by thermal distortion, it moves with slidably contacted with the inner periphery of the outer tube 103; therefore a large friction loss is caused.

[0014] While the inner tube 102 has appropriate dimensions for supporting the lenses 105, the diameter of the outer tube 103 is much larger than that of the inner tube 102 to carry the bimetal 104 in the space between the outer tube 103 and itself; therefore the projection lens unit 101 grows in size, taking large space.

[0015] (3) In the projection lens unit 101 of the above-mentioned construction, the inner tube 102 carrying the lenses 105 cannot be replaced; therefore there is no compatibility with other lenses.

[0016] (4) Where the inner tube 102 can move only within a limited range, the ability of compensation is limited.

[0017] (5) Where the inner tube 102, the outer tube 103, the bimetal 104, the guide member 107 and the like are complicatedly constructed, assembly thereof is difficult.

[0018] (6) Where only one piece of bimetal 104 is provided between the inner tube 102 and the outer tube 103 it is not easy to accurately move the inner tube 102; dimensional accuracy is difficult to be achieved.

[0019] (7) Where the bimetal 104 does not easily transfer heat, the response to temperature compensation becomes poor.

SUMMARY OF THE INVENTION

[0020] The present invention has been accomplished in view of the above-mentioned problems, and it is an object of the invention to provide a projection lens unit which is small, compatible and highly capable of compensating for changes in temperature.

[0021] In order to accomplish the above-mentioned object, according to the present invention, a projection lens unit comprises a lens unit body 6 for projecting an image light from the side of image light source, a plurality of leg portions which secure lens unit body to the side of image light source on the periphery of the lens unit body, and a plurality of expansion/contraction bars for compensating for the effect of heat, which are provided between the leg portions and the lens unit body with one end thereof engaged with the tip end side of the leg portions and the other end with the base end side of the lens unit body.

[0022] In the construction mentioned above, as the temperature increases and the leg portions begin to expand toward the tip end side, the expansion/contraction bars concurrently begin to expand toward the base end side. On the contrary, as the temperature decreases and the leg portions begin to contract toward the base end side, the expansion/contraction bars concurrently begin to contract toward the tip end side. The dimensions and material of the expansion/contraction bars are selected in consideration of various conditions, so that the changes in characteristics and the like induced by thermal expansion or thermal contraction of the leg portions and the lens unit body would be compensated for by thermal contraction or thermal expansion of the expansion/contraction bars in the reverse direction.

[0023] In the above-mentioned projection lens unit, it is desirable that the coefficient of thermal expansion of the expansion/contraction bar is different from those of the lens unit body and the leg portion.

[0024] In the construction mentioned above, when the expansion/contraction bars, the lens unit body, and the leg portions are respectively distorted by heat, the expansion/contraction bars having the different coefficient of thermal expansion from other members compensate for the changes of the lens unit body and the leg portions.

[0025] In the above-mentioned projection lens unit, it is desirable that the leg portions are supported on the projection lens unit body at more than two places.

[0026] In the construction mentioned above, where the leg portions support the lens unit body at more than two places, compensation for the changes induced by thermal contraction or thermal expansion is achieved evenly at more than two places. Meantime, when the lens unit body is supported at only two places, it is desirable that another member is provided to support the lens unit body so that the lens unit body can stably slide. It is desirable that the leg portions are evenly spaced. When the leg portions are provided at more than three places to support the lens unit body, the lens unit body 6 can be stably supported with these three legs alone, and therefore any additional member is not required to support the lens unit body. As described in the above, by supporting the projection lens unit body with the leg portions provided at more than three places, automatic compensation is achieved with high accuracies.

[0027] In the above-mentioned projection lens unit, it is desirable that the lens unit body comprises an outer lens-barrel which is directly supported on the leg portions mentioned above, an inner lens-barrel housed in the outer lens-barrel, and one or a plurality of lenses attached to inside the inner lens-barrel.

[0028] In the construction mentioned above, the outer lens-barrel, which supports the inner lens-barrel to which the lenses are attached, is secured to the side of image light source by the installation of the leg portions.

[0029] In the above-mentioned projection lens unit, it is desirable that latches or latch engaging slots are provided on the leg portions, and latch engaging slots or latches with which the above-mentioned latches or latch engaging slots are engaged are provided on the lens unit body, where the latch engaging slots are designed to be longer than the latches.

[0030] In the construction mentioned above, the leg portions are mounted on the lens unit body by engaging the latches with the latch engaging slots, and at the same time, the leg portions are allowed to axially slide in relation to the lens unit body through the shift of the latches in relation to the latch engaging slots, thereby achieving the compensation mentioned above.

BRIEF DESCRPTION OF THE DRAWINGS

[0031]FIG. 1 is a perspective view showing a base end portion of a lens unit body and leg portions according to the preferred embodiment of the present invention.

[0032]FIG. 2 is a sectional side view of a conventional projection lens unit.

[0033]FIG. 3 is a sectional side view showing a CRT and a first projection lens unit according to the preferred embodiment of the present invention.

[0034]FIG. 4 is a front view showing the first projection lens unit according to the preferred embodiment of the present invention.

[0035]FIG. 5 is a sectional side view showing a CRT and a second projection lens unit according to the preferred embodiment of the present invention.

[0036]FIG. 6 is a sectional side view showing the CRT and the second projection lens unit according to the preferred embodiment of the present invention.

[0037]FIG. 7 is a front view showing the second projection lens unit according to the preferred embodiment of the present invention.

[0038]FIG. 8 is a main fragmentary enlarged sectional view showing the leg portion according to the preferred embodiment of the present invention.

[0039]FIG. 9 is a side view of the leg portion according to the preferred embodiment of the present invention.

[0040]FIG. 10 is a plan view of the leg portion according to the preferred embodiment of the present invention.

[0041]FIG. 11 is a front view of the leg portion according to the preferred embodiment of the present invention.

[0042]FIG. 12 is a bottom view of the leg portion according to the preferred embodiment of the present invention.

[0043]FIG. 13 is a plan view of an expansion/contraction bar according to the preferred embodiment of the present invention.

[0044]FIG. 14 is a sectional side view showing the expansion/contraction bar according to the preferred embodiment of the present invention.

[0045]FIG. 15 is a plan view showing an engagement hole of the expansion/contraction bar according to the preferred embodiment of the present invention.

[0046]FIG. 16 is a sectional side view showing the engagement hole of the expansion/contraction bar according to the preferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0047] Referring now to the drawings, a preferred embodiment of a projection lens unit according to the present invention will be described in detail below. In the following description, it is assumed that the projection lens unit is incorporated in a projector. Two types of projection lens units will be presented herein as examples.

[0048] In a projector, an image which is formed on a CRT 1 is magnified by a projection lens unit 2 and projected onto a screen portion (not shown) as shown in FIG. 3 to FIG. 7. Accordingly, the projection lens unit 2 is directly fixed to the CRT 1. In concrete terms; the CRT 1 and a coupler 5 of the projection lens unit 2 are integrally secured by CRT support fittings 3 (refer to FIG. 6). The front surface of the CRT 1 (left surface in FIG. 3) is formed into a flat plane on which the coupler 5 is mounted.

[0049] A first projection lens unit 2 is shown in FIG. 3 and FIG. 4. The projection lens unit 2 is a member for projecting the image, which has been formed on the CRT 1, onto a screen portion by focusing thereto. The projection lens unit 2 is comprised of a coupler 5, a lens unit body 6, a plurality of leg portions 7 and a plurality of expansion/contraction bars 8.

[0050] The coupler 5 is comprised of an outer cylindrical portion 11, a C element 12 and a cooling liquid 13. The outer cylindrical portion 11 is formed into generally a thick cylinder with its base end (right end side in FIG. 3) being attached and mounted on the periphery of the front surface of the CRT 1. On the inner periphery of the base end surface of the cylindrical portion 11, a circular groove 15 is formed, to which a seal ring 16 is provided. The seal ring 16 is provided in order to seal the space between the base end of the outer cylindrical portion 11 and the front surface of the CRT 1. On the outer periphery of the base end of the cylindrical portion 11, a plurality of outer cylindrical portion support legs 18 (refer to FIG. 6) is provided, forming an integral part of the above-mentioned CRT support fitting 3. On the tip end of the cylindrical portion 11, a flange portion 19 is formed with its diameter inwardly reduced. At the outer side (tip side) of the inner periphery of the flange portion 19, a circular groove 20 is formed. The circular groove 20 is formed through an isolation groove 21. The isolation groove 21 is a member for reducing the contact area in order to alleviate the effect of heat. A seal ring 22 provided on the circular groove 20 is attached and mounted on the C element 12, thereby sealing inside the outer cylindrical portion 11. On the outside surface of the flange 19, a plurality of support tables 24 (refer to FIG. 7) is provided. The support tables 24 are provided for securing and supporting the leg portions 7 through the C element retaining plates 27. The support tables 24 are provided with their surface being raised from the surrounding area. Four support tables 24 are equally spaced, and a screw-receiving hole 25 is provided to each support table 24 into which a mount screw 28, which will be described later, is screwed.

[0051] The C element 12 is a member for defining a concave lens together with the front surface of the CRT 1, the outer cylindrical portion 11 and the cooling liquid 13. The C element 12 is formed into generally a hollowed circle or an oval by its cross section. A flange portion 26 formed into a flat ring is provided on the periphery of the C element 12. The flange portion 26 is attached and mounted on the seal ring 22 of the above-mentioned circular groove 20, thereby sealing inside the outer cylindrical portion 11. The flange portion 26 is fixed to the outer cylindrical portion 11 by the C element retaining plates 27, each of which is formed into a flat ring. The C element retaining plates 27 are secured to the support tables 24 by mount screws 28.

[0052] The cooling liquid 13 is an integral part of the concave lens of the coupler 5, which is provided for absorbing heat from the CRT 1. The cooling liquid 13 is filled in the space which is sealed by the outer cylindrical portion 11, the C element 12, the front surface of the CRT 1 and two pieces of seal rings 16 and 22, thus defining the concave lens.

[0053] The lens unit body 6 is a member for projecting the image formed on the CRT 1 onto the screen by controlling the light from the CRT 1. The lens unit body 6 is comprised of one or a plurality of lenses 31, an inner lens-barrel 32 and an outer lens-barrel 33.

[0054] The lenses 31 are composed of a combination of a plurality of concave lenses or convex lenses, which are selected in accordance to the design.

[0055] The inner lens-barrel 32 is a member for accurately supporting each lens 31 on its designated position. On the inside surface of the inner lens-barrel 32, lens support portions 34 are provided with the designated spacing so as to support each lens 31. On the periphery of the inner lens-barrel 32, frictional contact portions 35 are provided to which the inner lens barrel 32 comes into frictional contact when it appears and disappears from the outer lens barrel 33 while being supported by the outer lens-barrel 33. The inner lens-barrel 32 is supported by the outer lens-barrel 33 at the frictional contact portions 35 and secured to the outer lens-barrel 33 by a focus lock screw 46 which will be described later. The inner lens-barrel 32 is designed to be detached from the outer lens-barrel 33 just by removing the focus lock screw 46 so that it is replaced by another inner lens-barrel 32 of a different design. Thus, where the outer lens-barrel 33 responding to various types of CRTs 1 is arranged, it is possible to respond to various types of CRTs 1 by installing an inner lens-barrel 32 corresponding to respective CRT 1. Also, where various types of inner lens-barrels 32 are prepared for the identical outer lens-barrel 33 for replacement, it is possible to arrange various designs of lens unit body 6 to the CRT 1. Further, on the periphery of the inner lens-barrel 32, a nut portion 36, into which the focus lock screw 46 is screwed, is provided outwardly extending to the position where it contacts with the inner periphery of the outer lens-barrel 33. The inner lens-barrel 32 is supported by the outer lens-barrel 33 alone and it does not contact with the coupler 5.

[0056] The outer lens-barrel 33 is a member for housing and slidably supporting the inner lens-barrel 32, while being secured to the coupler 5. On the inside surface of the outer lens-barrel 33, an inner lens-barrel support portion 38 is provided which frictionally contacts with the frictional contact portions 35 of the inner lens-barrel 32. Accordingly, the outer lens-barrel 33 supports the inner lens-barrel 32, and it allows the movement of appearance and disappearance of the inner lens-barrel 32. The outer lens-barrel 33 is secured to the outer cylindrical portion 11 of the coupler 5 through the leg portions 7. In other words, the outer lens-barrel 33 is not directly secured to the outer cylindrical portion 11 but is secured through the leg portions 7.

[0057] On the periphery of the base end of the outer lens-barrel 33, a plurality of leg engaging recessed portions 41 is provided to which the leg portions 7 are mounted. Each leg engaging recessed portion 41 is formed into a recessed square corresponding to the shape of the leg portion 7 and a plurality thereof is equally spaced at four places in a circumferential direction. Close to the four corners of each leg engaging recessed portion 41, latch-engaging slots 42 are respectively provided. The latch-engaging slots 42 are openings for engaging and supporting each latches 58 of each leg portion 7 which will be described later. Each latch-engaging slot 42 is sized to be slightly longer than the width of the latch 58 so that the lens unit body 6 supported by the leg portions 7 can move in the direction of the optical axis. This allows the lens unit body 6 to deviate in the direction of the optical axis through the compensation by the expansion/contraction bars 8. On the base end of each leg engaging recessed portion 41 (bottom part in FIG. 1), a columnar support boss 43 is provided. The support boss 43 is a member for supporting the expansion/contraction bar 8 by engaging with one of engagement holes 62 of the expansion/contraction bar 8 which will be described later.

[0058] On the peripheral surface of the outer lens-barrel 33, an elongated slot 45 is provided, to which a focus lock screw 46 is inserted. The focus lock screw 46 inserted through the elongated slot 45 is screwed into the nut portion 36, in turn mounted on the inner lens-barrel 32 side. The elongated slot 45 is obliquely molded so that the inner lens-barrel 32 could rotate in relation to the outer lens-barrel 33 and the focus lock screw 46 would move within the elongated slot 45, thereby allowing the movement of appearance and disappearance of the inner lens-barrel 32 in respect to the outer lens-barrel 33, thus enabling an adjustment of the focal length.

[0059] A second projection lens unit 2A is shown in FIG. 5 to FIG. 7. The second projection lens unit 2A is generally the same as the projection lens unit 2 mentioned above. In order to respond to a smaller CRT 1A, the diameter of an outer cylindrical portion 11A of a coupler 5 is designed to be small in this unit. Accordingly, the isolation groove 21 is omitted. The basic construction of the second projection lens unit 2A is generally the same as that of the projection lens unit 2, notwithstanding a slight difference between the two models. The construction of the leg portion 7 is totally identical in these two models.

[0060] As shown in FIG. 9 to FIG. 12, the leg portions 7 are members for supporting the lens unit body 6 on the CRT 1 side through the coupler 5. Each leg portion 7 is comprised of a bottom plate 48, standing plates 49, a center plate 50, a support boss 51 and an expansion/contraction bar holding portion 52.

[0061] The bottom plate 48 is a member to be directly attached and mounted on the outer cylindrical portion 11. Each bottom plate 48 is provided with a screw-receiving hole 53, thereby mounted on the outer cylindrical portion 11 with the mount screw 28. Below the screw-receiving hole 53, a raised portion 54 is provided. The raised portion 54 is attached and mounted on each support table 24 through a C element retaining plate 27 with the mount screw 28.

[0062] Two pieces of the standing plates 49 are provided on both sides of the center plate 50. Each standing plate 49 is molded into generally a triangle with its width narrowing toward the front (upward). This construction gives a sufficient strength to the leg portion 7 without taking large space. The standing plates 49 are integrated with the bottom plate 48 at their bottom and each of which is also integrated with the center plate 50.

[0063] At the side of the outer lens-barrel 33 of the standing plates 49, a plurality of latches 58 and retaining nails 59 is provided. The latches 58 are members for supporting the leg portions 7 to the outer lens-barrel 33 side by engaging with the latch-engaging slots 42 of the leg engaging recessed portions 41. The width of each latch 58 (the horizontal dimension in FIG. 9) is set to be smaller than the length of each latch-engaging slot 42 of the leg engaging recessed portion 41 so that the leg portions 7 could move up and down (the vertical direction) when being engaged with the leg engaging recessed portions 41. This construction is employed in order to absorb the changes induced by thermal expansion. At the outer lens-barrel 33 side of the standing plates 49, the retaining nails 59 are provided throughout the entire periphery except for where the latches 58 are provided. These retaining nails 59 are provided in a manner that they embrace the expansion/contraction bar 8 from both ends. These retaining nails 59 of each standing plate 49 and the center plate 50 together form the expansion/contraction bar holding portion 52. The expansion/contraction bar holding portion 52 is a member for supporting the expansion/contraction bar 8 while allowing thermal expansion and thermal contraction thereof. In other words, by allowing thermal expansion and contraction of the expansion/contraction bar 8 which is supported by the expansion/contraction bar holding portion 52, the spacing of each support boss 43, 51 is adjusted in accordance with temperature changes.

[0064] The center plate 50 and each standing plate 49 together form a H-shape in its plane view. This configuration provides the leg portion 7 with sufficient strength. On the surface of the center plate 50 at the outer lens-barrel 33 side, the support boss 51 is provided. The support boss 51 is a member for supporting the expansion/contraction bar 8 by engaging with the engagement hole 62 of the expansion/contraction bar 8.

[0065] The expansion/contraction bar 8 is a member for absorbing the effect of thermal expansion and thermal contraction. In other words, this member absorbs various effects of heat such as deviation of the lens unit body 6 in relation to the CRT 1 or expansion of the lenses 31 induced by thermal expansion and thermal contraction, in order to project clear images onto the screen with a predetermined focus. The expansion/contraction bar 8 is composed of a rectangular plate, as shown in FIG. 13 to FIG. 16. At both ends of the expansion/contraction bar 8, engagement holes 62 are provided, with each of which support boss 43, 51 is engaged respectively. The inside diameter of each engagement hole 62 is designed to be slightly larger than the outside diameter of the support boss 43 and 51. On the inner periphery of each engagement hole 62, raised support streaks 63 are provided. The raised support streaks 63 are members for stably supporting the support boss 43, 51 which have been inserted into the engagement hole 62 respectively. Three raised support streaks 63 are equally spaced on the periphery of each support boss 43, 51 along with the axis. In this construction, each raised support streak 63 stably supports the support boss 43, 51 from three directions. Taper provided on the rim of the engagement holes 62 allows easy insertion of the support boss 43 and 51.

[0066] The expansion/contraction bars 8 are mounted on the expansion/contraction bar holding portions 52 with each support boss 43, 51 inserted to the engagement holes 62 respectively. The material and dimensions of the expansion/contraction bar 8 are selected in accordance with such parameters as heating value of the CRT 1, ambient temperature, thermal expansion value of the leg portion 7 and the lens unit body 6. Specifically, the material and dimensions of the expansion/contraction bar 8 are determined so as to achieve the coefficient of linear thermal expansion (the change) effective to absorb the thermally induced changes such as expansion or contraction of the coupler 5, the lens unit body 6, and the leg portions 7, resulted from heating of the CRT 1. Accordingly, the coefficient of linear thermal expansion of the expansion/contraction bar 8 is set to be different from those of the lens unit body 6 and the leg portion 7. In concrete terms, the coefficient of linear thermal expansion of the expansion/contraction bar 8 is set to the value in which the combined thermal changes of the lens unit body 6 and the leg portions 7 are absorbed, thereby compensating for the changes of the lens unit body 6 and the leg portions 7. The coefficient of linear thermal expansion of the expansion/contraction bar 8 is selected in an individual and concrete manner by way of experiments and the like so as to achieve the coefficient of linear thermal expansion as mentioned above. The dimensions of the expansion/contraction bar holding portion 52 are determined in accordance with the expansion/contraction bar 8. As practical material of the leg portion 7 and the expansion/contraction bar 8, polycarbonate, polypropylene and the like are used.

[0067] Now, assembly of the lens unit body 6 of the projection lens unit 2 in the above-mentioned construction will be described below.

[0068] First, the expansion/contraction bars 8 are attached to the expansion/contraction bar holding portions 52 of the leg portions 7. The expansion/contraction bars 8 are held onto the expansion/contraction bar holding portions 52 by being pushed into between the retaining nails 59, with one of the engagement holes 62 being engaged with the support boss 51. Thereafter, the leg portions 7 are mounted on the leg engaging recessed portions 41 of the lens unit body 6. The latches 58 of the leg portions 7 are inserted to the latch-engaging slots 42 of the leg engaging recessed portions 41 for engagement. Accordingly, the other engagement hole 62 of the expansion/contraction bar 8 is engaged with the support boss 43 of the leg engaging recessed portion 41.

[0069] Thereafter, the leg portions 7 are positioned on the support tables 24 of the outer cylindrical portion 11 through the C element retaining plates 27, and the mount screws 28 are inserted from the screw-receiving holes 53 on the bottom plates 48 of the leg portions 7 to be screwed down to the screw-receiving holes 25. Accordingly, the lens unit body 6 is secured to the coupler 5 through the leg portions 7.

[0070] In the projection lens unit 2 of the above construction, the effect of heat is absorbed as described below.

[0071] Heat generated by the CRT 1 in use of the projector or heat of ambient temperature is transferred to the lens unit body 6, causing each portion to go through thermally induced changes such as thermal expansion. In this occasion, the leg portions 7 and the expansion/contraction bars 8 also go through thermal expansion. The leg portions 7 expand toward the tip end side of the projection lens unit 2. On the other hand, the expansion/contraction bars 8 expand relatively toward the base end relative to the leg portions 7 when being heated, because the engagement hole 62 thereof at the tip end side is engaged with the support boss 51 of each leg portion 7, thus preventing relative position of the lens unit body 6 to the coupler 5 from deviating in thermal expansion, and the expansion/contraction bar 8 expands so that the lens unit body 6 would be positioned at the optimum place.

[0072] Meanwhile, when replacing the lens of the projection lens unit 2 with another lens of a different design, the inner lens-barrel 32 should be replaced. Accordingly, a variety types of the inner lens-barrels 32 should be prepared beforehand. In replacing the lens, the inner lens-barrel 32 is removed from the outer lens-barrel 33 of the lens unit body 6 and another type of inner lens-barrel is introduced thereto. Replacement of the lens to another design is completed just by this operation.

[0073] As described in the above, because the expansion/contraction bars 8 correct the outer lens-barrel 33 by changing themselves in accordance with the thermally induced changes of the leg portions 7 or the lenses 31 and the like, it is possible to obtain an automatic compensation with high accuracies. In other words, because the unit is equipped with the expansion/contraction bars 8 provided between the leg portions 7 and the lens unit body 6 for compensating for the effect of heat, with each one end engaged with the tip end side of the respective leg portions 7 and the other end with the base end side of the lens unit body 6, the property changes of the leg portions 7 and the lens unit body 6 induced by thermal expansion or thermal contraction can be compensated for the expansion/contraction bars 8 through the changes thereof in the reverse direction, thereby allowing an accurate and automatic compensation.

[0074] Because the expansion/contraction bar 8 has the coefficient of linear thermal expansion which is different from those of the lens unit body 6 and the leg portion 7, the property changes of the lens unit body 6 and the leg portions 7 when induced by heat can be compensated for by the expansion/contraction bars 8 with the different coefficient of linear thermal expansion. As a consequence, automatic compensation with high accuracies is achieved.

[0075] Further, in the construction in which the latch-engaging slots 42 are configured to be longer than the latches, the leg portions 7 are mounted on the lens unit body 6 through the engagement of the latches 58 with the latch-engaging slots 42, and at the same time, they are allowed to axially slide when the latches 58 deviate in relation to the latch-engaging slots 42. Accordingly, the compensation is made by thermal contraction or thermal expansion of the expansion/contraction bars 8, thus enabling automatic compensation with high accuracies.

[0076] Also, since the lens unit body 6 is supported by the leg portions 7 at four places in the unit, the lens unit body 6 is stably secured, and at the same time compensation by thermal contraction or thermal expansion is evenly made at four places, enabling automatic compensation with high accuracies.

[0077] Further, the latches 58 and the latch-engaging slots 42 absorb the changes induced by thermal expansion or thermal contraction, thus prohibiting the aging of the projection lens unit 2 and improving the reliability thereof.

[0078] Moreover, the construction in which the expansion/contraction bars 8 are attached to the expansion/contraction bar holding portions 52 of the leg portions 7 does not take large space, and consequently making the projection lens unit 2 compact.

[0079] Where the inner lens-barrels 32 of a variety design of lenses and the outer lens-barrel 33 of different shapes are prepared for the appropriate replacement, it is possible to respond to a variety type of CRTs 1 and at the same time provide the projection lens unit 2 with various performances.

[0080] In addition, the assembly of the unit is easy because the leg portions 7 can be installed to the lens unit body 6 just by retaining the expansion/contraction bars 8 to the expansion/contraction bar holding portions 52 of the leg portions 7, and engaging the latches 58 of the leg portions 7 with the latch-engaging slots 42 of the leg engaging recessed portions 41 while the engagement holes 62 at one end of the expansion/contraction bars 8 are engaged with each support boss 51 of the respective leg portion 7.

[0081] Since the expansion/contraction bars 8 are practically adhered to the outer lens-barrel 33 of the lens unit body 6 and the leg portions 7, the changes thereof substantially coincide with the temperature changes of the outer lens-barrel 33 and the leg portions 7, thus achieving a better response and the optimum compensation for temperature changes.

[0082] In the lens unit body 6 which is comprised of the inner lens-barrel and the outer lens-barrel, the outer lens-barrel is fixed to the side of image light source by the leg portions. This configuration reduces the diameter of the outer lens-barrel and consequently the unit would be downsized.

[0083] Although four pieces of the leg portions 7 are provided on the periphery of the outer lens-barrel 33 in the above-mentioned embodiment, two, three or more than five pieces of the leg portions 7 may be also provided.

[0084] When only two leg portions 7 are provided to support the lens unit body 6 and the lens unit body 6 cannot stably slide, it is desirable that another member is provided to support the lens unit body 6 so that the lens unit body 6 can stably slide. If the lens unit body 6 can stably slide in this construction, no additional measure is required. In the example mentioned above, it is possible to slidably support the lens unit body 6 in a stable manner by engaging the latches 58 of the leg portions 7 with the latch-engaging slots 42 of the leg engaging recessed portions 41 and not providing all the expansion/contraction bars 8 corresponding to the respective leg portions. In the example mentioned above, the expansion/contraction bars 8 may be removed from two facing legs 7 out of four legs and compensate for the changes using the expansion/contraction bars 8 on the remaining legs 7. Also, other means including a sliding rail, a slider and the like may be provided to stably slide the lens unit body 6.

[0085] When more than three pieces of leg portions 7 are provided to support the lens unit body 6, and the lens unit body 6 can be stably supported by these legs alone any other member is not required for sliding the lens unit body. In this construction, the leg portions 7 which are provided to the lens unit body 6 at more than three places can stably support the lens unit body 6, and at the same time the changes induced by thermal expansion or thermal contraction can be evenly compensated for at more than three places.

[0086] When two, three or five pieces of the leg portions 7 are provided and compensation is made by the expansion/contraction bars 8, the leg portions 7 provided with the expansion/contraction bars 8 should be positioned so as to obtain even compensation. Although the leg portions 7 do not need to be equally spaced as long as even compensation can be achieved, generally it is desirable that the leg portions 7 are equally spaced. This achieves automatic compensation with high accuracies.

[0087] Although the lens unit body 6 is comprised of the inner lens-barrel 32 which supports the lenses 31, and the outer lens-barrel 33 which supports the inner lens-barrel 32 in the above-mentioned embodiment, the present invention may be applied to the lens unit body which is comprised of the outer lens-barrel 33 only. The present invention can be also applied to the lens unit body in which the outer lens-barrel 33 supports the lenses 31 and thermally induced problems are similarly caused therein. In this case also, the same operation and advantageous effect of the invention may be obtained as in the above-mentioned embodiment.

[0088] Although the latches 58 are provided to the leg portions 7 and the latch-engaging slots 42 to the outer lens-barrel 33 of the lens unit body 6 in the above-mentioned embodiment, these members may be provided in a reverse way, i.e. to provide the latches 58 to the outer lens-barrel 33 of the lens unit body 6 and the latch-engaging slots 42 to the leg portions 7. In this case also, the same operation and advantageous effect of the invention can be obtained as in the above-mentioned embodiment.

[0089] Although the projection lens unit 2 is used in a projector in the above-mentioned embodiment, it may be also used in other types of optical apparatus. Also, the present invention may be applied not only to the CRT 1 but also to the liquid crystal screen. In this case also, the same operation and advantageous effect of the invention as in the above-mentioned first embodiment can be obtained.

[0090] Although two engagement holes 62 are provided to each expansion/contraction bar 8 so as to be engaged with each of the support bosses 43 and 51 in the above-mentioned embodiment, more than three engagement holes 62 may be also provided to each expansion/contraction bar 8 in order to respond to the case where the positions of the support boss 43, 51 are varied. Otherwise, a plurality of expansion/contraction bars 8 with different dimensions may be prepared beforehand in accordance with the positions of the support boss 43, 51. The positions of the support boss 43 and 51 may be also changed accordingly so as to provide an appropriate compensation in accordance with the changes in temperature of the CRT 1 and the ambient temperature. In this case also, the same operation and advantageous effect of the invention can be obtained as in the above-mentioned first embodiment.

[0091] Although the leg portions 7 are supported on the outer lens-barrel 33 by engaging the latch-engaging slots 42 with the latches 58 in the above-mentioned embodiment, the leg portions 7 may be supported on the outer lens-barrel 33 with each expansion/contraction bar 8 being fixed to each leg portion 7 at one end and one engagement hole 62 of each expansion/contraction bar 8 at the base end being engaged with the support boss 43 at the outer lens-barrel 33 side. The leg portions 7 thus supported on the outer lens-barrel 33 at more than three places do not create a frictionally contact portion, thereby improving accuracies and also preventing aging. 

1. A projection lens unit comprising a lens unit body for projecting an image light from a side of image light source, a plurality of leg portions for fixing said lens unit body to the side of image light source on the periphery of the lens unit body, and a plurality of expansion/contraction bars for compensating an effect of heat, which are provided between said leg portions and said lens unit body with one end engaged with the tip end side of the leg portion and the other end with the base end side of the lens unit body.
 2. The projection lens unit according to claim 1, wherein said expansion/contraction bar has a coefficient of linear thermal expansion which is different from those of said lens unit body and said leg portion.
 3. The projection lens unit according to claim 1, wherein said leg portions support said lens unit body at more than two points.
 4. The projection lens unit according to claim 2, wherein said leg portions support said lens unit body at more than two points.
 5. The projection lens unit according to claim 1, wherein said lens unit body comprises an outer lens-barrel which is directly supported by said leg portions, an inner lens-barrel housed inside said outer lens-barrel, and one or a plurality of lenses attached to inside said inner lens-barrel.
 6. The projection lens unit according to claim 2, wherein said lens unit body comprises an outer lens-barrel which is directly supported by said leg portions, an inner lens-barrel housed inside said outer lens-barrel, and one or a plurality of lenses attached to inside said inner lens-barrel.
 7. The projection lens unit according to claim 3 wherein said lens unit body comprises an outer lens-barrel which is directly supported by said leg portions, an inner lens-barrel housed inside said outer lens-barrel, and one or a plurality of lenses attached to inside said inner lens-barrel.
 8. The projection lens unit according to claim 4, wherein said lens unit body comprises an outer lens-barrel which is directly supported by said leg portions, an inner lens-barrel housed inside said outer lens-barrel, and one or a plurality of lenses attached to inside said inner lens-barrel.
 9. The projection lens unit according to claim 1, wherein said leg portions are provided with latches or latch engaging slots, said lens unit body is provided with latch engaging slots or latches to which said latch engaging slots or latches are inserted, and said latch engaging slots are formed longer than said latches.
 10. The projection lens unit according to claim 2, wherein said leg portions are provided with latches or latch engaging slots, said lens unit body is provided with latch engaging slots or latches to which said latch engaging slots or latches are inserted, and said latch engaging slots are formed longer than said latches.
 11. The projection lens unit according to claim 3, wherein said leg portions are provided with latches or latch engaging slots, said lens unit body is provided with latch engaging slots or latches to which said latch engaging slots or latches are inserted, and said latch engaging slots are formed longer than said latches.
 12. The projection lens unit according to claim 4, wherein said leg portions are provided with latches or latch engaging slots, said lens unit body is provided with latch engaging slots or latches to which said latch engaging slots or latches are inserted, and said latch engaging slots are formed longer than said latches.
 13. The projection lens unit according to claim 5, wherein said leg portions are provided with latches or latch engaging slots, said lens unit body is provided with latch engaging slots or latches to which said latch engaging slots or latches are inserted, and said latch engaging slots are formed longer than said latches.
 14. The projection lens unit according to claim 6 wherein said leg portions are provided with latches or latch engaging slots, said lens unit body is provided with latch engaging slots or latches to which said latch engaging slots or latches are inserted, and said latch engaging slots are formed longer than said latches.
 15. The projection lens unit according to claim 7, wherein said leg portions are provided with latches or latch engaging slots, said lens unit body is provided with latch engaging slots or latches to which said latch engaging slots or latches are inserted, and said latch engaging slots are formed longer than said latches.
 16. The projection lens unit according to claim 8, wherein said leg portions are provided with latches or latch engaging slots, said lens unit body is provided with latch engaging slots or latches to which said latch engaging slots or latches are inserted, and said latch engaging slots are formed longer than said latches. 